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Bryant, Matthew

Abstract

The rapid proliferation of wireless sensors and microelectronics has spurred considerable interest in developing small scale devices that convert ambient energy sources to electrical power. Such "energy harvesting" devices could thus eliminate the need for hardwired power and extend the useful lifespan of a wireless sensor beyond the finite capacity of a battery. Piezoelectric materials, which directly convert mechanical strain to electrical energy, have been extensively investigated in recent years as a potential means to harvest energy from mechanical vibrations. This research has predominately focused on harvesting energy from preexisting vibrating host structures through base excitation of cantilevered piezoelectric beams. This approach, while simple to implement, inherently restricts the application of piezoelectric energy harvesting technology to environments where suitable vibrations are available. This dissertations proposes and investigates a novel piezoelectric energy harvesting device that simultaneously generates vibrations and harvests energy from an ambient fluid flow by inducing an aeroelastic flutter instability in a simple structure. The proposed device is studied through a combination of analytic modeling and wind tunnel experimentation. A model of this device that captures the three-way coupling between the structural, unsteady aerodynamic, and electrical aspects of the system is developed. The model is applied to predict the flow speed required for energy harvesting using linear stability analysis, and is generalized to account for aerodynamic nonlinearities that lead to flutter limit cycle behavior over a broad range of flow speeds. Wind tunnel test results are presented to determine empirical aerodynamic model coefficients and to characterize the power output and flutter frequency of the harvester as functions of incident wind speed. The model is then used to investigate the key design parameters of the system and determine the sensitivity and effective range of each parameter in affecting the characteristics of the aeroelastic instability driving the energy harvester. Finally, wind tunnel testing and flow visualization investigate the aerodynamic interactions between multiple flutter energy harvesters operating simultaneously. These experiments reveal synergistic wake-structure interactions than can be used to enhance the array performance, allowing the harvesters to produce more power when operating in close proximity than in a steady free stream flow.